This invention relates generally to water filtration systems. More particularly, the invention is directed to filtration systems that include gravity filters that are periodically backwashed.
Gravity filters used to filter water commonly include a filter top chamber, a filter medium at the bottom of the filter top chamber, and a filter bottom chamber. Influent is received in the filter top chamber, and passes through the filter medium before being collected and removed through a filter effluent line. Flow through the filter medium slows as the medium becomes filled with waste, or it takes more pressure to force the same flow rate through the dirty filter media. Thus, the medium is periodically cleaned to increase the rate of flow or decrease the required pressure.
It is known that the medium can be cleaned by backwashing. Backwashing generally involves stopping the supply of influent to the filter top chamber and adding pressure to the liquid in the filter bottom chamber, causing the direction of flow through the medium to be reversed. The dirty water is then removed from the filter top chamber and discharged through a separate line.
It is conventional for a facility to have multiple filter cells to prevent interruption of filtration while one of the filter cells is being backwashed. In such facilities, the filter influent line can be divided into separate branches leading to each of the filter cells, with valves on each branch enabling the operator to shut off the flow to any selected cell while that cell is backwashed. Separate lines from each cell are used to discharge backwashed water.
Pressure for backwashing may be supplied by a backwash supply pump, or from the hydraulic head in the other filter cells or in a separate backwash supply tank or standpipe. Systems are conventionally designed so that the volume of liquid needed to backwash a cell is provided by operating the remaining filter cells at design rates. It has been known that increasing the height of the top chambers of the filter cells allows additional liquid volume to be stored in the cells, permitting backwashing to occur even when the system is operating at less than design conditions.
The invention relates to a new vertical pipe gallery that may be shop-built to significantly facilitate the connections and piping used in water filtration systems. The pipe gallery includes an exterior peripheral wall containing a gallery upper chamber, a backwash waste chamber, and a gallery lower chamber. A gallery influent line and a plurality of filter influent pipes are connected to the gallery upper chamber. A backwash drain line and a plurality of secondary pipes are all connected to the backwash waste chamber. A plurality of filter effluent pipes and a gallery effluent line are all connected to the gallery lower chamber.
In one embodiment of the invention, the lower chamber also contains a separate supply chamber, to which a gallery backwash supply line and a plurality of filter backwash pipes are connected.
The pipe gallery may be used in a liquid filtration system containing a plurality of conventional filter cells, each filter cell comprising a filter top chamber, a filter medium at the bottom of the filter top chamber, and a filter bottom chamber beneath the filter medium. The filter influent pipes and secondary pipes are connected to the top chambers of the filter cells, and the filter effluent pipes are connected to the bottom chambers of the filter cells.
To filter water, valves are used to open a filtering pathway that extends from the gallery influent line through the gallery upper chamber and the filter influent pipes to one or more of the top chambers of the filter cells. From there, the water flows through the filter medium into the lower chamber of the filter cells, then through the filter effluent pipes and the lower chamber of the gallery and to the gallery effluent line. Other valves are used to isolate the backwash drain line from the filtering pathway and to isolate any gallery backwash supply line from the filtering pathway.
To backwash a filter cell, valves are used to open a backwash pathway from the gallery lower chamber to the bottom chamber of the filter, through the medium and into the top chamber of the filter. From there, the water flows through an associated secondary pipe and the backwash waste chamber to the backwash drain line. Valves isolate the filter effluent line and the gallery upper chamber from the backwash pathway while the backwashing process is underway. When a separate backwash supply chamber is provided, the backwash pathway begins in the backwash supply chamber and reaches the filter through the filter backwash pipe associated with the filter cell being backwashed.